It might be just a coincidence but after draining my oil and switching to mobile1s synthetic, my temp. gauge started to fluctuate when I drove my car. I noticed that when Im driving normally the temp. is where it was normally, a bar below the middle of the gauge; but as soon as I stop and let the engine idle, the temp. slowly climbs up as high as the H. I dont understand what could had happened during my oil change, I didnt tamper with anything else. If anyone has any ideas Id greatly appreciate them, thanks.

 

your thermostst is either crapped out or has air bubble stuck in it
check your coolant level/system

car year/model/mileage might help a little